“Which I found odd but I really didn’t ask; it wasn’t any of my business. But looking back at it now, I guess there was something else going on.”

Adam Lanza opened fire in two Sandy Hook Elementary classrooms on Friday in Newtown, Conn., gunning down 20 first-graders and kindergarteners and six educators.

Lanza ended the carnage by blowing his brains out with a single shot to the head.

Kraft, himself a former Sandy Hook School student, said he was overwhelmed after learning the kid he once cared for would turn out to be one of the nation’s most despised killers.

“I just couldn’t think for a little while. I was shaking,” he said.

The former babysitter also remembered Lanza as quiet, intelligent, introverted and highly focused on the task at hand.

“Whenever we were doing something, whether it was building Legos, or playing video games, he was really focused on it. It was like he was in his own world,” Kraft said.

Despite Nancy Lanza’s warning to Kraft to keep a suspicious eye on little Adam, that didn’t stop the mom from sharing her of guns with her son.

Lanza took her son to shooting ranges so they could hone their skills together. She was Adam Lanza’s first victim on Friday, fatally shooting her before continuing the bloodshed at Sandy Hook Elementary.

Cops vowed today to trace every moment of the killer’s life to understand what led him to commit Friday’s atrocities.

“We will go back to the date of [Adam Lanza’s] birth,” Connecticut State Police Lt. Paul Vance said today.

“We will answer every single question determining any kind of medical condition any kind of issues whatsoever that he may have been involved in.”

Vance vowed: “We will cover every single facet [of Lanza’s life].”

Local and state cops had no previous contact with the killer before Friday, according to Vance.

Authorities also disclosed today there were two adults who were shot — but not killed — in Friday’s bloodshed.

It had been previsouly reported there was only one wounded, surviving adult at Sandy Hook Elementary.

“The faculty and staff in that school did everything they possible could to protect those children,” Vance said.

“I can tell you the first responders that got to that scene, the active shooter team, that entered that school and saved many human lives. Now I can tell you, it broke our hearts that we couldn’t save them all.”